The general plan of the structure of the nervous system is described by its two components: central and peripheral. The brain and spinal cord belong to the central nervous system, and cranial, autonomic and spinal nerves are the basis of the peripheral.
Man, like all other living organisms, is able to respond to chemical and physical changes in the environment.
There are environmental factors (touch, sound, light, and smell) that are converted into nerve impulses using special sensitive cells. Those, in turn, are represented by a series of electrical and chemical changes directly in the nerve fiber. The resulting impulses are transmitted through afferent fibers to the brain and spinal cord, where necessary commands are generated for transmission via efferent (motor) fibers to the muscles responsible for the executive function.
The structure and functions of the nervous system are aimed at integrating external influences with the body's ability to adapt to it.
The structure of the nervous system cannot be considered completely without a description of its structural unit - a neuron, which is a nerve cell and consists of a body, a nucleus, dendrites (branched processes) and an axon (one long process). The principle of operation of the neuron - along dendrites, nerve impulses pass to the body of the cell, then through the axon it goes to effectors or other cells.
Between themselves, neurons are connected through the processes using a synapse, the role of which is to filter nerve impulses. He is able to pass some impulses and delay others.
Neurons can belong to various groups that determine their specific function. So, neurons of one group perform an analytical function and are responsible for the fragmentation of a nerve impulse. The second group is responsible for the synthesis and determination of impulses coming from other senses. There is a third group, which keeps the consequences from previous influences and compares the emerging effects with traces.
The control center of a complex network of nerves distributed throughout the human body is the spinal cord, which has the appearance of a long white “rope”, a finger thick, up to 45 cm long and weighing about 30 g, and is located in the spinal canal. It consists of two components - gray matter (accumulation of nerve cells) and white matter (nerve fibers).
To the left and to the right of the spinal cord, spinal nerves branch out in the form of branches from the tree trunk. It is they that are directed to various parts of the human body and provide a relationship with the central nervous system. Control over a certain "area" of the body is carried out by such a separate nerve.
The spinal nerve consists of the posterior, or sensory, and the anterior, or motor, bundles. The first type of fiber originates from the receptors of the skin, tendons, muscles, joints, internal organs and sensory organs. It is in the receptors that nerve signals appear that contain information about events occurring both in the body itself and from the outside. These signals are sent through the back fibers to the spinal cord, and from there to the brain, where they are sorted, processed, evaluated, and other signals sent to the muscles, internal organs, and vessels in response to the front fibers.
The structure of the nervous system may include the autonomic nervous system, which is responsible for metabolism and the functioning of internal organs. A feature of this system is its independent functioning and at the same time submission to the central nervous system.
In its effect on internal organs, the autonomic nervous system consists of parasympathetic and sympathetic systems. Their relationship is quite complicated, since often they have the opposite effect on the same organ, due to which a certain balance in the body is achieved.
The structure of the nervous system includes the cerebral cortex, which has a thickness of about 3 mm and a total area of about a quarter sq.m. This part of the organ has six layers, the cells of which are closely interconnected with each other. The total number of these cells is about 15 billion.
The structure of the nervous system It will not be considered completely without such a phenomenon as a reflex, which is a reaction of the body to internal and external effects with the help of the central nervous system. Reflexes are subdivided into conditioned (the body's ability to adapt to changing environmental conditions) and unconditioned (an innate reaction to external stimuli). Unconditioned reflexes do not require certain conditions for their development, and conditioned reflexes arise under the influence of various phenomena that are vital for a person.